There is an increasing demand by consumers for nutritious foods that improve physical performance, reduce risks of disease, and increase life span. Researchers and food manufacturers are interested in increasing polyphenols and particularly anthocyanins in foods, due to the antioxidant properties of these compounds and their role in the prevention of various diseases, such as many types of cancer, cardiovascular and neurodegenerative diseases (1-5). In addition, anthocyanins have anti-inflammatory activity, improve visual acuity, modulate the immune response and hinder obesity and diabetes (6-8).
Since these health-promoting effects depend on relatively high level of anthocyanins, there is a strong need to increase their amounts in human diet. Blueberries are one of the richest sources of anthocyanins and are highly recommended for human consumption (10). However, despite its beneficial properties, blueberry consumption per capita is still low compared to other types of fresh fruits and vegetables. In addition, blueberries contain high amounts of sugar, which may not be desirable for many individuals. Thus, there is a need to develop other plants with increased anthocyanins and total polyphenol content, with less sugar, that could gain wide popularity among public, and can become part of everyday food intake.
Lettuce (Latuca sativa L) is widely used in salads and sandwiches, and is an important component in human diet and nutrition. Recently, lettuce was the second most consumed fresh vegetable in the USA behind potatoes (9). Red lettuce cultivars could be relevant as dietary sources of natural antioxidant compounds, anthocyanins and other polyphenols. Anthocyanins accumulate in cell vacuoles of lettuce and are responsible for pigmentation from red to dark purple color. However, most of red lettuce cultivars, especially head forming types, are not typically red throughout the leaves. In many cases, they are only red along the leaf edges or speckled with red. The synthesis of anthocyanins in lettuce is induced by light, especially UV-radiation (16-17); therefore, the red color is expressed in those parts of plants that are exposed to daylight and UV-radiation.
Recent studies have shown that amounts of polyphenols and anthocyanins produced in different red lettuce cultivars under various light intensities, growth conditions and temperature were significantly lower than in blueberry (11-15).